1. Field of the Invention
The present invention relates to antenna arrays. More specifically, the present invention relates to slotted waveguide and broadband antenna arrays.
While the present invention is described herein with reference to illustrative embodiments for particular applications, it should be understood that the invention is not limited thereto. Those having ordinary skill in the art and access to the teachings provided herein will recognize additional modifications, applications, and embodiments within the scope thereof and additional fields in which the present invention would be of significant utility.
1. Description of the Related Art
As is well known, many conventional missile target detection and tracking systems employ active radar. In such systems the missile radar typically illuminates a target with pulsed radiation of a predetermined frequency and detects the return pulses. Unfortunately, the bandwidth of such active radar systems is typically only approximately three percent of the frequency of the illuminating radiation. The narrow bandwidth of conventional active radar increases susceptibility to jamming. In particular, if an intended target vehicle can discern an approximate frequency range within which the operative frequency of the active radar is included, the target may "jam" the radar by saturating it with large quantities of radiation within this range. These emissions may prevent the active radar from discriminating the return pulses from the radiation transmitted by the jamming vehicle, which may allow the intended target to evade the active radar. Moreover, utilization of active radar discloses the location thereof to the intended target.
A target tracking system complementary to that of active radar is known as broadband anti-radiation homing (ARH). Broadband ARH systems are passive. That is, ARH systems do not illuminate a target with radiation, but instead track the target by receiving radiation emitted thereby. Consequently, an intended target may not frustrate an ARH system simply by emitting radiation as such emissions aid an ARH system in locating a target. Additionally, employment of an ARH system does not reveal the position thereof to the intended target. Nonetheless, an ARH system is generally of utility only to those instances wherein an intended target emits an appreciable quantity of radiation.
As may be evident from the above, a target tracking system incorporating both an active radar and a passive ARH system would be foiled much less easily than one constrained to function in an exclusively active or passive mode. Missiles, however, typically have an extremely limited amount of "forward-looking" surface area available on which to mount antennas associated with either an active radar or broadband ARH system. Consequently, attempts have been made to devise antenna arrays--operative through a single antenna aperture--for both active and passive target tracking.
A first approach to such a single aperture system entails deploying an array of broad frequency bandwidth radiating elements together with a broadband feed network. However, these arrays have limited efficiency, and thus low gain, due to losses in the broadband circuits included therein. Thus, when operative in the active radar mode these circuits typically lack the high efficiency and power capabilities of conventional active radar. In a second unitary aperture approach, active target tracking and passive target identification are attempted to be effected by suspending broadband dipole elements above an active radar array. Unfortunately, such an approach is unsuitable for broadband passive target tracking due to the small number of dipole elements which may be included within the antenna aperture.
Hence, a need in the art exists for an antenna system operative through a single antenna aperture which is capable of functioning simultaneously in active radar and passive broadband modes.